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    SubjectRe: [PATCH 40/42] perf callchain: Save eh/debug frame offset for dwarf unwind
    Em Thu, Jan 29, 2015 at 05:07:21PM +0900, Namhyung Kim escreveu:
    > When libunwind tries to resolve callchains it needs to know the offset
    > of .eh_frame_hdr or .debug_frame to access the dso. Since it calls
    > dso__data_fd(), it'll try to grab dso->lock everytime for same
    > information. So save it to dso_data struct and reuse it.
    >
    > Note that there's a window between dso__data_fd() and actual use of
    > the fd. The fd could be closed by other threads to deal with the open
    > file limit in dso cache code. But I think it's ok since in that case
    > elf_section_offset() will return 0 so it'll be tried in next acess.

    Thanks, applied after rewriting the changelog to read as:

    ---
    perf callchain: Cache eh/debug frame offset for dwarf unwind

    When libunwind tries to resolve callchains it needs to know the
    offset of .eh_frame_hdr or .debug_frame to access the dso.

    Since it will always return the same result for a given DSO, just
    cache the result as an optimization.
    ---

    - Arnaldo


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